An encoder, such as a linear encoder or rotary encoder, is an electro-mechanical device that converts the position or motion of a shaft or other mechanical machinery to an analog or digital code. Both linear and rotary encoders may be suited for applications in machine control which demand reliable and accurate position and/or motion feedback. Linear encoders, for instance, may be used in metrology instruments, high precision machining tools, and motion systems, such as gantry tables and cranes. And rotary encoders may be used to determine an angular position of a robotic joint, for instance, such as a joint of a robotic arm. Linear and rotary encoders may take the form of relative (or incremental) linear/rotary encoders and absolute linear/rotary encoders.
An output of a relative encoder provides information about motion of the shaft, which can be further processed into information such as speed, distance, and position. A relative encoder records changes in position, but may not have a predetermined relationship between its state and a position of the shaft. Some devices controlled by relative encoders may have to “home” to a fixed reference point of the relative encoder in order to determine such a position.
On the other hand, an output of an absolute encoder indicates a current position of the shaft. An absolute encoder maintains position information (i.e., encodes position values) even when power is removed from the absolute encoder, such that the position information can be available immediately upon applying power to the absolute encoder. A relationship between the position information and a position of the shaft may be established during assembly of the absolute encoder.